The present invention relates to a method and a device for cutting a metal strip which runs out from a hot-rolling mill train, especially at particularly high speed. The metal strip is cut by shears arranged downstream of the hot-rolling mill train. A driver having two driver rollers is arranged downstream of the shears. The metal strip runs through the driver rollers.
In hot rolling, special requirements exists with respect to the cutting of metal strips, since hot rolling takes place at high strip speeds. Consequently, the cutting of a hot-rolled strip must be carried out at a high strip speed, as well. Due to the cutting at high speeds, an extremely short time is available for changing over from the conditions during the threading out of the front strip to the conditions necessary for threading in the rear strip. In particular, the speed of the driver rollers downstream of the shears downstream of the shears must change very quickly. Therefore, the drivers are required to have extremely low inertia. However, these requirements can only be met partially so that narrow limits are set on the cutting of hot-rolled strips with respect to the strip speed. During the cutting of fast metal strips, particularly when working with strips running out from a roll stand at a speed above 12 m/sec, a particular problem lies in the repercussions on the rolling process upstream of the shears.
Japanese Patent JP 8 90058 describes a method for cutting a metal strip in which, subsequent to the cutting, rollers arranged downstream are opened for passing the strip. British Patent No. GB 20 73 080 and Japanese Patent No. 4 171116 describe cutting of rolled strip which runs out from a mill train at high speed.
An object of the present invention is to provide a method for cutting fast-running metal strips from a hot strip mill. Repercussions on an upstream mill train by the cutting of the metal strip are prevented or significantly reduced.
In the method according to the present invention, driver rollers on both sides of the shears are utilized. In the sequence of phases according to the present invention, the driver rollers downstream of the shears can be opened or closed subsequent to the cutting, the front tension then being guaranteed by the driver rollers upstream of the shears. In this manner, repercussions on the upstream rolling process due to the cutting can be prevented to the greatest possible extent. Thus, quality impairments of the rolled metal strip due to the cutting operation can be reduced. Cutting is now possible at high speeds, as well, without requiring parameters which cannot or only difficulty be achieved from a standpoint of mechanical engineering to be adjusted at the drivers.
In the present invention, the processes are decoupled by reducing the front tension in the metal strip between the driver rollers and the coiler prior to opening the driver rollers. In this manner, a particularly smooth strip run is achieved. Finally, the present invention has the advantage that the front tension of the metal strip between the driver rollers and driver rollers arranged upstream of the shears is reduced to a necessary minimum tension prior to cutting the metal strip. This further reduces the repercussions of the cutting on the rolling process, and results in a particularly accurate cut.
In this context, the necessary minimum tension is the tension in the metal strip which is required for the metal strip to be tightened and to be able to be cut.
In an example embodiment of the present invention, the rear metal strip resulting from the cutting of the metal strip is grasped by the coiler subsequent to opening the driver rollers. After the rear metal strip is grasped by the coiler, the driver rollers may be closed.
In the example device according to the present invention, driver rollers are provided upstream of and downstream of the shears. In this manner, in connection with the present invention, a particularly good decoupling between cutters and rolls is achieved. Advantageously, provision is made for a computing device which is connected to all system components via a data link.